The U.S. Pat. No. 4,621,672 issued to this inventor of the present invention discloses a horizontal Venetian blind comprising a plurality of upper slats and lower slats, whose bevels are separately controlled. The Venetian blind is provided with two sets of mechanisms to control the upper group of slats and the lower group of slats. The device comprises a movable stem 36 which is fastened at the top end thereof with the spring plate 40, and at the bottom end thereof with a hand operated lever 43. The movable stem 36 is provided with a gear 37 which is engaged with the internal gear 34a of the worm 34 for driving the worm wheel 32. At the time of the downward pulling, the gear 37 is engaged with the gear 35a of the worm rod 35 for driving the worm wheel 33. The worm wheels 32 and 33 are coupled with two shafts 21 and 22, which can be driven to turn at will. Such a prior art device as described above can not be produced in quantity at a low cost.